In recent years, plants have been increasingly used as a host system for the expression of recombinant proteins. Such expression can be accomplished either by integrating the gene of interest into a plant genome, to create a transgenic plant that stably expresses the desired protein, or by introducing the gene of interest into a plant vector that can be introduced into, and transiently maintained in, plant cells. Viral vector systems have proven to be particularly useful.
However, there remains a need for developing improved systems for expressing transgenes in plants. For example, one disadvantage with existing viral vector systems is that the viruses may infect non-target plants, potentially posing significant environmental risks. Also, many available engineered plant viruses do not express transgenes at desired levels, and/or in desired target plants or tissues. The present invention addresses many of these problems, and others.